Photo Dynamic Therapy (PDT) is a method of treatment in which active oxygen or the like is generated by a chemical reaction that arises when a photosensitive substance with an affinity for an abnormal cell or a tumor is irradiated with light of a specific wavelength and the abnormal cell or the tumor is necrotized by a bactericidal activity of the active oxygen. Much attention has been recently drawn from a viewpoint of QOL (Quality Of Life) because a normal cell is not damaged.
Meanwhile, laser is mainly used as a light source used for the PDT. A reason therefor is, for example, that the laser is monochromatic light and is able to effectively excite a photosensitive substance having a narrow absorption band, that the laser has high light intensity density, and that the laser is able to generate pulse light. However, laser light is normally spot light, has a narrow radiation coverage, and hence is not suitable for treatment of skin disease or the like.
In recent years, a group of Professor Daisuke Tsuruta, Instructor Toshiyuki Ozawa, et al. of Osaka City University Graduate School of Medicine has presented the first success in the world in treatment of a Methicillin-resistant Staphylococcus aureus (MRSA) infected skin ulcer by conducting systemic administration of 5-aminolevulinic acid (ALA) that is natural amino acid and the PDT using LED light with a wavelength of 410 nm (refer to NPL 1). The ALA is a precursor of a porphyrin-based compound in a heme biosynthetic pathway, and does not provide photosensitizing properties by itself. When a given amount of hemes is produced, physiologically, biosynthesis of the ALA is inhibited by a negative feedback mechanism. However, when exogenous ALA is excessively administered, the negative feedback mechanism is invalid, ferrochelatase that is a rate limiting enzyme in heme biosynthesis is depleted, and a large amount of biologically-inherent porphyrin-based compounds, particularly, protoporphyrin IX (PpIX) is accumulated in a cell. In the PDT using the ALA, the PpIX is used as a photosensitizing substance. Such a method of treatment does not cause new resistant bacteria, and is hence expected as a new method of treating bacterial infection in the modern medicine in which there is difficulty in treatment of resistant bacteria.
Meanwhile, NPL 1 discloses an absorption spectrum of PpIX. It is described that light absorption peaks of the PpIX are at positions with wavelengths of 410 nm, 510 nm, 545 nm, 580 nm, and 635 nm.
The phototherapy is generally utilized for various objects of treatment for disease such as neonatal jaundice, psoriasis, or acne, alleviation of pain, cosmetics, and the like. Green light and blue-white light are used for treatment for neonatal jaundice, ultraviolet light is used for treatment for psoriasis, and blue light, red light, and yellow light are used for treatment for acne. Red light is used for treatment for early-stage lung cancer (stage 0 or stage 1 lung cancer), superficial esophageal cancer, superficial early-stage gastric cancer, initial cervical cancer, and dysplasia. In this manner, various light sources are used in accordance with intended use.
In order to spread such a technique, a light irradiating device capable of uniformly radiating light to affected parts having various three-dimensional shapes and sizes is required.
A device using a light source such as an excimer lamp or an arc lamp, a device using laser as a light source, a device of a system in which therapeutic light is radiated planarly by using an optical fiber, and the like have been known as the existing light irradiating device.